Hayward Sand Filter Blowing Sand Into the Pool? Causes and Fixes (W3S166T)
You turn the pump on and a cloud of grit shoots out of the return jet. Then it settles on the pool floor, you brush it, and it comes right back the next day. It is one of the more annoying pool problems because vacuuming does nothing until you deal with the filter itself.
Sand in the pool is not a mystery. It means sand is getting past something it should not be getting past. On a Hayward ProSeries filter like the W3S166T, there are only a few places that can happen.
Why is my Hayward sand filter blowing sand into the pool?
In almost every case a lateral is cracked or a standpipe has come loose. Those parts sit at the bottom of the tank and act as a screen. When one breaks, sand walks straight through the filter and into your return lines.
The usual suspects, roughly in order of how often we see them:
- A cracked or split lateral at the bottom of the tank
- A standpipe that cracked or separated from the lateral assembly
- The wrong sand was used, usually play sand instead of #20 silica
- Too much sand in the tank, so it spills over into the multiport valve
- A worn spider gasket in the multiport valve letting sand bypass into the return
One thing to rule out first: if the filter is brand new or you just changed the sand, a little dust for a day or two is normal. Fresh silica sand carries fine powder. Backwash for two or three minutes, rinse, and see if it clears up on its own.
How do I know if it's a lateral or the multiport valve?
Watch where the sand shows up. Sand at the return jets points to a lateral or standpipe problem inside the tank. Sand going out the waste line during filter mode points to the multiport valve.
A quick check: set the valve to filter and run the pump while watching the backwash line. If sand runs out of the waste port when it should be closed, the spider gasket in the valve is the problem, not the laterals. That is a much cheaper fix.
If sand only shows up in the pool and the waste line stays dry, you are opening the tank.
How to fix a sand filter that's putting sand in the pool
This is a half day job on a W3S166T. Nothing here is complicated, but it is physical work and you will be scooping wet sand out of a tank.
- Shut off the pump at the breaker and open the air relief valve on top of the filter
- Close the valves on either side of the filter, then drain the tank using the drain cap at the base
- Remove the multiport valve from the tank, being careful not to snap the standpipe
- Scoop the old sand out. A wet vac or a plastic cup and patience both work
- Inspect every lateral. Look for hairline cracks, split slots, and any lateral that has come unthreaded
- Check the standpipe for cracks, especially near the bottom where it meets the hub
- Replace whatever is broken, tape the top of the standpipe shut, and refill with fresh #20 silica sand to the fill line
- Reinstall the valve with a new tank o-ring, backwash for a few minutes, rinse, then return to filter
Use only #20 grade silica pool filter sand. Play sand from a hardware store is too fine and will pass right through the laterals on a W3S166T no matter how good the parts are.
Should I repair the filter or replace it?
If the tank is solid and only a lateral or two is cracked, repair it. Parts are cheap and the filter will last years more.
Replace the filter when the tank itself is cracked, when the threads where the valve mounts are stripped or chewed up, or when the unit is fifteen plus years old and you are already paying for sand, laterals, and a valve rebuild. At that point you are spending most of the cost of a new filter to keep an old one alive.
Sizing matters too. A 16 inch tank like the W3S166T is sized for above ground pools and smaller setups. If your filter has always struggled to keep up and it is undersized for your pump, replacing it with the right size solves two problems at once.
How do I keep it from happening again?
Backwash on pressure, not on schedule. When the gauge reads eight to ten PSI above your clean starting pressure, backwash. Doing it constantly wears the valve gasket faster and washes sand out over time.
Change the sand every five to seven years. Old sand rounds off, channels, and stops filtering well, and it also puts more strain on the laterals. And never let the pump run dry, since the pressure spike when water slams back into an empty tank is one of the fastest ways to crack a lateral.
If your W3S166T is past saving, here is the same filter new:
Not sure this is the right part for your problem? Reach out and we will help you figure out exactly what you need before you spend money on the wrong thing.